Photovoltaic power plants are becoming practical as grid scale generation facilities capable of producing tens of megawatts, decreasing the cost of photovoltaic modules. Larger plants are being built to satisfy mandates for renewable energy capacity. Penetration levels of photovoltaic plants are expected to be significant. Photovoltaic plants may produce short term, rapidly changing (e.g. as much as 100% of rated power per minute or 200% of rated power per minute) variable output power that may be due to shading caused by isolated moving clouds. For this reason, energy producers and grid operators may consider large photovoltaic power plants (i.e. larger than 2 MW) to be unpredictable.
Stability, reliability, and power quality of the electric grid, which may be negatively affected by large photovoltaic power plant variability, is controlled by allocating reserve generation capacity for load following, spinning reserve, voltage support, and frequency regulation with hydro, steam, and combustion turbine generators that can respond relatively faster than base load power generation plants such as coal and nuclear type plants. Reserve generation resources may not have the response characteristics needed to account for short term variability of large solar photovoltaics.
Reducing short term variability of large solar photovoltaics would reduce the need for reserve generation. Large photovoltaic plants connected at utility grid distribution level (69 kV and less), may introduce voltage deviations and flicker depending upon the capacity and impedance of the network or feeder. Reducing short term variability would reduce voltage effects and/or permit voltage regulation devices to react.